Add heuristics to skip thumbnail generation when it's unnecessary.

chrome/browser/history/top_sites_cache.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/history/top_sites_cache.h"
 
 #include "base/logging.h"
 #include "base/ref_counted_memory.h"
 
 namespace history {
@@ skipping 29 matching lines @@
                                      scoped_refptr<RefCountedBytes>* bytes) {
   std::map<GURL, Images>::const_iterator found =
       images_.find(GetCanonicalURL(url));
   if (found != images_.end()) {
     *bytes = found->second.thumbnail.get();
     return true;
   }
   return false;
 }
 
+bool TopSitesCache::GetPageThumbnailScore(const GURL& url,
+                                          ThumbnailScore* score) {
+  std::map<GURL, Images>::const_iterator found =
+      images_.find(GetCanonicalURL(url));
+  if (found != images_.end()) {
+    *score = found->second.thumbnail_score;
+    return true;
+  }
+  return false;
+}
+
 GURL TopSitesCache::GetCanonicalURL(const GURL& url) {
   CanonicalURLs::iterator i = TopSitesCache::GetCanonicalURLsIterator(url);
   return i == canonical_urls_.end() ? url : i->first.first->url;
 }
 
 bool TopSitesCache::IsKnownURL(const GURL& url) {
   return GetCanonicalURLsIterator(url) != canonical_urls_.end();
 }
 
 size_t TopSitesCache::GetURLIndex(const GURL& url) {
@@ skipping 41 matching lines @@
     const GURL& url) {
   MostVisitedURL most_visited_url;
   most_visited_url.redirects.push_back(url);
   CanonicalURLEntry entry;
   entry.first = &most_visited_url;
   entry.second = 0u;
   return canonical_urls_.find(entry);
 }
 
 }  // namespace history